Wikipedia:Reference desk/Archives/Science/2007 November 26

= November 26 =

Fire Accelerants
Are there any fire accelerants that aren't immediately lethal when consumed in considerable quantities? I know drinking a cup of gasoline will be unpleasant, but is there something that doesn't kill you, unless you then swallow a match or something... 74.230.231.13 (talk) 00:04, 26 November 2007 (UTC)


 * It depends on your definition of fire accelerant. From the article, "an accelerant is any substance or mixture that "accelerates" the development of fire", I think bottles of pure oxygen will accelerate a fire very quickly, but won't immediately kill you. --antilivedT 02:12, 26 November 2007 (UTC)


 * Define "considerable" - almost anything will kill you if consumed in high enough quantities. Many spirits are flammable, as demonstrated by party tricks such as flaming sambuca; and I expect something like an overproof rum would serve as an accelerant - according to our article, a mix of water & ethanol with over about 50% ethanol is flammable, so a spirit which is in the 60-70% ABV range should go up easily enough (although it's drinkability is another matter...) -- AJR | Talk 02:14, 26 November 2007 (UTC)
 * Some substance such as vegetable oil, ghee, or glycerol are actually food items and will also accelerate a flame. Others such as wax may not be food, but are fairly harmless to eat. Graeme Bartlett (talk) 07:56, 26 November 2007 (UTC)

Murder
In response to the answers above, my friend says, "OK, so we are going to get someone to OD on it and then shoot them with a flaming arrow." But I don't think that would work. Would the [alcohol, glycerol, ghee, oil] remain flammable after being introduced into the stomach? H YENASTE 23:19, 27 November 2007 (UTC)


 * In sufficient quantities to perpetrate arson? I doubt that, but also doubt that the substance would catch on fire, would there be enough oxygen present to allow it? Also, the substance in question, when being reacted on by the stomach acid may not be flammable either. 68.39.174.238 (talk) 03:45, 28 November 2007 (UTC)

Balancing a chemical equation with silver nitrate copper and water
Alright I have this problem. I disolved .0185 moles of silver nitrate into a unkown amount of water to form a solution. I then dissolved 2.81 grams of copper oixide water into the solution until there was 1.25 grams left. I need to write the chemical equation for it if the copper is suppose to be +2 and +1 in charge. Does anyone know how to do that? —Preceding unsigned comment added by 70.249.230.252 (talk) 00:26, 26 November 2007 (UTC)


 * It sounds like homework or schoolwork help. The question also seems to have a typo ("2.81 grams ... until there was 1.25 grams left"). Just try writing out your reaction equation: the question is asking to use two forms: cupric and cuprous oxide, which are CuO and Cu2O, respectively. SamuelRiv (talk) 02:03, 26 November 2007 (UTC)

Kinetic energy released by expansion of space
If space is expanding everywhere then the space in which all solid bodies exist must be expanding. As it expands the bodies themselves do not because the atoms that make up the body are attracted to each other and the nuclear forces keep the particles at a constant distance.

But this must mean that the atoms, if effect, move downhill a to keep that constant distance and, as such, there is a conversion of potential energy to kinetic energy.

Has anyone calculated the rate of kinetic energy being imparted to the earth as a result of the expansion of space?

Also, where does this energy come from? Or is this question completely off base?

Doug Moffat

209.5.192.16 (talk) 00:34, 26 November 2007 (UTC)

Energy doesn't come from anything. It cannot be created or destroyed but can only change energy types of change into matter. I'm not sure what you mean when you say there is a conversion of potential energy to kinetic due to space expanding. I'm not sure if that actually occurs, because space expanding has little effect on the bodies occupying that space, it just causes the bodies to move away from each other, yet still retain there current position in space. Space (which is not matter) is expanding and doesn't really effect the matter. —Preceding unsigned comment added by 70.249.230.252 (talk) 00:55, 26 November 2007 (UTC)


 * No, the point is a fair one. Anon is basically saying that if we take two massive bodies stuck to each other by gravity, inflation will try to pull them apart. If it succeeds, then you suddenly have gravitational potential energy that can be exploited if you stopped inflation for a second. Unfortunately, stopping inflation is the only scenario in which that energy can be exploited, so the end effect is just an effectively lower force between objects, if I'm reading this right. That is part of the reason we need dark matter: we find that certain clusters are not being pulled apart like they should be, so obviously the gravity in the cluster is higher than that due to visible mass. SamuelRiv (talk) 02:37, 26 November 2007 (UTC)
 * Space is only expanding between galaxies that are far apart and have very little gravitational influence on each other. Where matter exists, space does not expand (I think).  Although your point is still valid (I think) because there would still be some gravitation force between them however small.  Does the energy come from vacuum energy?  Shniken1 (talk) 06:07, 26 November 2007 (UTC)
 * I don't believe that's correct. From what I understand, space is expanding evenly throughout the universe.  In fact, if portions did not expand evenly, then that would either warp space or require that other sections expand faster to make up for the non-expanding portions.  Expansion is slow, and gravitation can usually hold objects together despite space expanding.  Of course with gravity, the closer together the objects are, the stronger it is.  So, far apart objects, like galaxies, are more affected by expansion than the objects in a solar system would be.  Essentially, gravity helps prevent the objects from expanding, but not space from expanding.  While I don't see that explicitly stated there, you might try looking through metric expansion of space for more information on this topic. --  Hi  Ev  14:39, 26 November 2007 (UTC)
 * Absent a cosmological constant, the expansion is nothing more or less than objects moving away from each other. There's no outward pull on anything; it's just inertia. Space is only "expanding" in areas where things are still moving apart (i.e. far from galactic superclusters). I suppose you can think of the cosmological constant as adding a ubiquitous outward pull, but all this does, like any other (sufficiently small) source of tension, is perturb the object into a different equilibrium state. So maybe the ground-state energy of hydrogen is slightly (undetectably) different than it would be without a cosmological constant, but that can't be used as a source of energy because there's no lower energy state to push it into. -- BenRG (talk) 15:42, 26 November 2007 (UTC)
 * I think you're confusing the expansion of the universe with inflation. The universe is still expanding, but inflation, if it happened at all, ended 13.7 billion years ago. -- BenRG (talk) 15:42, 26 November 2007 (UTC)

The kinematics of dark energy can be reasonably well approximated by adding an extra force to the universe such that every object experiences an apparent Fdark = D*M*x, where D is a small constant, M is it's mass, and x is its distance from the observer. In other words, the apparent force is trivial at short range and large at great distances. It also follows that adding a small constant force, doesn't generate additional energy for an object like the Earth which is held together by much larger forces. Dragons flight (talk) 11:30, 26 November 2007 (UTC)

Two Point Function
I was reading this book awhile ago and it talked about something called the two point function. It was caused by two flucuations in a vacumm in space diverging until they became so close that their energy density matrices became infinite. Thus causing for the equation having to be renormalized, and this somehow caused an expansion in space-time. Does anyone know what I'm talking about or does this sound like nonsense? —Preceding unsigned comment added by 70.249.230.252 (talk) 01:01, 26 November 2007 (UTC)


 * Could it be Zero-point energy, and the related cosmological constant problem it apparently poses? -- Finlay McWalter | Talk 02:16, 26 November 2007 (UTC)


 * My bet is that it's the vacuum fluctuations of Edward Tyron that describes how the universe may have been created out of nothing. There is an excellent nontechnical overview of this here . It could also be bubble nucleation of a false vacuum, which is another common pre-inflationary scenario. SamuelRiv (talk) 02:26, 26 November 2007 (UTC)
 * Reading the link you provided SamuelRiv Inflation for beginners paragraph 4 reads:
 * If the Universe starts out with the parameter less than one, O gets smaller as the Universe ages, while if it starts out bigger than one O gets bigger as the Universe ages. The fact that O is between 0.1 and 1 today means that in the first second of the Big Bang it was precisely 1 to within 1 part in 1060). This makes the value of the density parameter in the beginning one of the most precisely determined numbers in all of science, and the natural inference is that the value is, and always has been, exactly 1. One important implication of this is that there must be a large amount of dark matter in the Universe. Another is that the Universe was made flat by inflation.
 * Now 1st sentence make sense. Then: how do we observe it to be smaller than 1? If it is anything from 0.1 to 1 (does it mean it's not precisely determined or that it varies localy?) today how do we calculate it would have been precisely close to 1 in the first second of the Big Bang? "the value is, and always has been, exactly 1", hang on didn't they just say it would be anything between 0 and 1? I'll carry on reading. Keria (talk) 10:34, 26 November 2007 (UTC)
 * Qualitatively, it is like O(t2) is approximately O(t1)^(s(t2)/s(t1)) where O(t) denotes O at time t, and s(t) is the size of the universe at time t. If O is approximately 0.5 now, then when the universe was 1/10 this size, O would have needed to be 0.5^(1/10) = 0.93.  To allow for an O roughly near 1 today, it implies that O was very, very near 1 in the distant past when the universe was very small.  An appealing solution is to posit that O is exactly 1 at all times.  Incidentally, if O is much different than 1, it would imply that the ultimate fate of the universe would already have been realized (either through collapse or run away expansion).  Hence O approximately 1 can also be looked at through the anthropic principle since we could not exist in a universe that was otherwise.  Dragons flight (talk) 11:06, 26 November 2007 (UTC)

Query related to Urine
Is there any harm (or what are the results), if a girl drinks a man urine mistakenly / willingly. —Preceding unsigned comment added by Ashish.k.garg (talk • contribs) 06:57, 26 November 2007 (UTC)


 * Amazingly, we have an article on this. Urophagia.  Someguy1221 (talk) 07:05, 26 November 2007 (UTC)


 * If the person in question doesn't have any diseases and is healthy, it should be ok. Urine straight out of the body is sterile. But it can be contaminated, and that's what causes that urine smell. 64.236.121.129 (talk) 15:53, 26 November 2007 (UTC)
 * I think the urine smell is due to the ammonia in the urine. 128.163.170.161 (talk) 17:39, 26 November 2007 (UTC)
 * There is no ammonia in urine. If there was, it would be unsafe to drink, which it isn't. Ammonia is converted into urea before it is excreted. 64.236.121.129 (talk) 14:44, 27 November 2007 (UTC)


 * The whole point of urination is to remove toxic substances from the blood e.g. excess salt, urea, uric acid, creatinine etc., so drinking it cannot be healthy in any large quantity (although it is sterile). And I once heard that cat's urine has ammonia Tomi P (talk) 22:51, 27 November 2007 (UTC)


 * Other than possibly consuming too much salt, there is nothing dangerous about urine. See Urophagia. Btw, we are talking about human urine, not cat urine. 64.236.121.129 (talk) 16:42, 28 November 2007 (UTC)


 * Actually as the article mentions (admitedly with a citation needed tag), you probably should take care if the person is taking medications Nil Einne 08:32, 1 December 2007 (UTC)

gide us
Dear sir,

We want to make one controlling project for university and we need some information and help for designig a pc bord or programing a one plc with this specification:
 * voltsge source:12 V
 * it sould be have 40-60 Switchs
 * and this equipmet sould be control with progaram and it's capacity is 2Km.
 * please send us yor guids and name of some company that can help us. —Preceding unsigned comment added by 91.184.66.107 (talk) 07:53, 26 November 2007 (UTC)
 * So to attempt to clarify, you want to remotely control something 2 kilometers away, by operating 40 to 60 switches at the remote position. What do you want to switch at the remote location - do you want relays?  Are you willing to run a copper pair or optic fibre between your controlling point and the remote device, or do you need a wireless system? Graeme Bartlett (talk) 08:01, 26 November 2007 (UTC)

GREATMIND Q ABT. DOG
can I detect pregnancy in dogs by a Hcg hormone pregnancy tester used in human females? —Preceding unsigned comment added by 59.95.178.103 (talk) 08:41, 26 November 2007 (UTC)


 * No, human pregnancy tests are useless in dogs. Dogs are an estrous species, rather than a menstrual one: dogs undergo the same hormonal changes whether pregnant or not. Dog pregnancies are traditionally "diagnosed" by ultrasound or palpation.... there is a blood hormone that is elevated in pregnant dogs, called relaxin, and a blood test is available for this, but it's useful only later in pregnancy than the human tests we're used to are. - Nunh-huh 08:56, 26 November 2007 (UTC)

Does being cold and wet, increase your chances of getting a virus like a cold or flu?
Why or why not? 64.236.121.129 (talk) 15:51, 26 November 2007 (UTC)


 * There have been studies that have found a correlation between being cold (or cold and wet) and catching a cold. I haven't seen such studies on the flu.  They are usually dismissed due to poor management of the control and test groups (or a complete lack of a control group).  In the U.S. NIH book, being cold or wet is not listed as a cause for the cold or the flu.  However, both are listed as "seasonal" - meaning that they occur predominantly during a certain time of the year.  Anyone who has kids knows that a lot of things pass from children to parents.  In the winter, we send kids to school where they share all kinds of things and then bring them home.  So, it is pretty much a no-brainer as to why there are more cold/flu issues during the children's school-year. --  k a i n a w &trade; 16:03, 26 November 2007 (UTC)
 * Why do these viruses exist during one time of the year, but not the others? 64.236.121.129 (talk) 16:07, 26 November 2007 (UTC)


 * Keeping everyone in close quarters (in the winter) makes it easier to spread viruses around. Plus, the lower relative humidity probably also makes it easier to become infected from a given number of virions.
 * Atlant (talk) 16:39, 26 November 2007 (UTC)


 * I don't know about that. I don't see complete strangers huddling around just because it's colder outside. How does lower humidity make it easier to become infected? 64.236.121.129 (talk) 17:03, 26 November 2007 (UTC)


 * You don't need to huddle, you just need to spend more time breathing in recirculated air. Haven't you ever seen waydowntown??
 * Atlant (talk) 17:32, 26 November 2007 (UTC)


 * No. No I have not. And people spend time in the same building through other seasons too. Whether you go to school or work, you are still spending time in a building with other people, through all the seasons. 64.236.121.129 (talk) 18:50, 26 November 2007 (UTC)


 * Did you read the first reply above? It is colder in the winter.  The school year tends to be in the winter.  Children spend more time around each other during the school year.  So... children are closer to more children when it is colder outside.  It is all about proximity.  The viruses don't gather super-virus strength from the cold.  They still need people to be close to one another to travel from host to host. --  k a i n a w &trade; 17:43, 26 November 2007 (UTC)
 * The school year is during part of the summer, fall, winter, and spring. It's not mostly in the winter. The only time school is out is during the summer, but the school year does extend to parts of the summer. Also, I question whether your assumption is correct. You are assuming children are the source. You are also assuming children are closer together during the winter. That's just speculation. Also how does one get the virus in the first place? In order to catch it from someone else, someone initially had to catch it. 64.236.121.129 (talk) 18:47, 26 November 2007 (UTC)


 * I know that the Wikipedia rules insist that we assume good faith, but I'm starting to feel like you've simply come here for an argument.


 * Atlant (talk) 19:01, 26 November 2007 (UTC)


 * Nope. Assume good faith. I'm just asking questions. 64.236.121.129 (talk) 19:31, 26 November 2007 (UTC)


 * So if people catch colds more during the Winter because they spend more time indoors with others, does that mean that in places such as Phoenix, Arizona where people spend more time indoors in the Summer, people get more colds in the Summer? Deli nk (talk) 18:56, 26 November 2007 (UTC)


 * You have a bit of a point there. Contrary to the OPs assumption that I'm just speculating, it is my job to manage health data for millions of patients.  There are exceptions, but the rule is that cold/flu cases spike in September.  That is when children go back to school.  They slowly go down until January when kids come back from the winter break (smaller spike than sept).  Then, they keep dropping and dropping until there are no significant number of cases by summer.  However, there are many cases of summer colds and flus (just not enough to be significant).  Comparing desert regions to non-desert regions, the percentage of people with summer cold/flu cases is higher in the desert regions.  While I don't have enough Phoenix patients in my database to draw a real conclusion for that particular city, I do have over three million patients Arizona and New Mexico - which is to my knowledge mostly desert.  So, you have some data to back up your claim that desert-dwelling people have higher rates of summer colds and flus.
 * To the OP... you appear to believe that cold/flu viruses go away and then come back. They don't go away.  In any large population, there is always someone with a cold/flu virus.  Most often, it is the children (again, I can look at the data and see that the younger the person the higher rate of having cold/flu diagnoses - so this is not just speculation).  To catch the cold/flu, you must be around someone who has it and have the virus physically travel from the other person to you and then successfully make it past your body's defenses and start multiplying.  At that point, you will risk infecting everyone around you.  The more people you have around you, the higher chance you have of infecting someone else.  That is why having people near each other is the key to spreading the cold/flu virus. --  k a i n a w &trade; 19:14, 26 November 2007 (UTC)


 * What about anecdotes like that one President of the United States who gave a really long inaugural address out in the cold and then died a few weeks later? Also, wasn't there an American football coach who was doused by the customary, celebratory cooler of Gatorade only to get sick and die afterward?  Besides frostbite and hypothermia, can exposure to the cold give you other problems?--The Fat Man Who Never Came Back (talk) 18:52, 26 November 2007 (UTC)


 * For the U.S. President, see William Henry Harrison.


 * Atlant (talk) 19:01, 26 November 2007 (UTC)


 * This is an interesting discussion (though I'm sure it's been discussed since time immemorial). Can being cold and wet give you, say, pneumonia or other conditions?--The Fat Man Who Never Came Back (talk) 19:38, 26 November 2007 (UTC)


 * Weakening your immune system when you have a cold/flu can lead to further complications - such as pneumonia. So, the question is, "Does being cold and wet weaken your immune system?"  I did a quick AMA search and found nothing on that topic.  I'm sure you can find many hits on Google - but not necessarily proper medical studies. --  k a i n a w &trade; 19:56, 26 November 2007 (UTC)


 * A lot of it is to do with heating systems, viruses like warmth as much as humans and any systems that recirculate air (such as that found in large buildings) is going to ensure the microbes get maximum circulation. The more people that get these bugs, the more carriers there are to ensure they keep spreading.  The start of the heating season always brings the bugs out. GaryReggae (talk) 21:43, 26 November 2007 (UTC)


 * You might want to try reading The Straight Dope article "Why is winter the season for colds, flu, etc.?" It explains that being cold or wet does not increase your chances of getting sick, and also notes that some "seasonal" illnesses are actually encountered at various times throughout the year, and that some factors such as cold stress, which can cause cold/flu-like symptoms, and seasonal psychological stress, which can weaken the immune system, may be adding to the winter cold/flu stats.  Hope that helps! --  Hi  Ev  22:50, 26 November 2007 (UTC)


 * Psychological stress can weaken the immune system? Has this been proven? My other question is, if it is true that one usually catches it from another person, how did patient 0 catch the cold in the first place? Just incompetance by touching dirty objects, then putting their hands in their mouth/nose? 64.236.121.129 (talk) 16:46, 27 November 2007 (UTC)


 * Yup, stress hormones from chronic stress can suppress the immune system. See Ask A Scientist - Stress and immune system.  As for your "patient 0", that person might have existed centuries ago, and the virus just keeps circulating through the population.  Or, as is the case with new flu viruses, existing viruses co-mingle and/or mutate in a host (pig, chicken, duck, human, etc.) and produce a new virus.  There are lots of ways viruses are created and spread, so there isn't just one answer to that question. --  Hi  Ev  19:47, 27 November 2007 (UTC)


 * Well, the being cold - catching cold connection may have some fact behind it. The thing is, when you're cold, your body tries to conserve heat, and keep the heat in, leaving less heat at the extremities. This can include your head, if it is not well covered. If you are wet, there is a good probability your hair will be too. When your head becomes cold, it starts to restrict blood flow, but of course not hinder it altogether. When this happens, your immune system in the cold area can decline, since the blood carries white blood cells. The area, in this case your head, becomes cold, but still warm enough for the viruses to develop. There are viruses all around us, but usually they are kept at bay by your white blood cells. The viruses and bacteria can now reproduce, because there aren't as many white blood cells to attack them. When you come back inside, the viruses are still there, but now more heat is induced, so the body no longer has to conserve, and the viruses multiply even faster, giving it time to spread, but now since the blood flow is increased, the white blood cells come back to attack the viruses. Now, your immune system will take care of the rest, so you usually don't get an automatic cold that way, but you may see the early symtoms of one: high head temperature, when the blood flow increases to get rid of the germs; runny nose, when the mucus attempts to wash away the viruses in your nose; sneezing, to get rid of viruses in your nasal system; coughing, to get rid of viruses in the throat; stuffy nose, caused by excess mucous and nasal activity, etc. So, the correlation may be there, but usually isn't as direct as you may think. Now, if you wear too much clothing outside on a cold day, it will increase your body heat substantially, but since your head is usually exposed, the temperature at the surface of your face may go down. This prevents large amounts of white blood cells from entering the area, but produces enough heat so that the viruses can multiply profusely. Plus, the excess clothing causes you to sweat, and wind can allow the cold to enter your body, potentially degrading your immune system. The numbing cold near the surface of your face, supplied with feeling by your warm interior, can cause pain in your face and sinuses, and possibly cause a headache. A risk of not wearing enough clothing in the cold is more of hypothermia than getting a cold. Plus, if you're not wearing excess clothing because you're going to be excersizing strenously, it could cause further complications. Excersize causes sweat to be produced, and the sweat, along with the wind and cold, can allow coldness to enter your body. I don't think this has been proven, but not tucking your shirt in can expose your stomach areas to the cold, and supplied with enough body heat, can allow invasive viruses to develop in the stomach and intestines, potentially causing diarrhea. Also, the sudden warming of extremities after coming inside might explain why my hands, for example, often feel warm instead of uncomfortably cold to the rest of my body. Remember that this is mostly theoretical, and science seems to want to reject any "myths" based on experience rather than scientific fact. Hope this helps. Thanks. ~ A H  1 (TCU) 21:59, 27 November 2007 (UTC)
 * Ok so now some statements are contradicting each other. Astro said viruses are around us all the time, so that means we can get infected even without being close to someone who is already infected. Which means the so called, patient 0 can be anyone who happens to catch a cold from the enviroment. But HiEv said patient 0 existed since the cold virus was first contracted, and has simply spread from person to person since then. This implies that one does not catch the cold from the enviroment, but rather from people. Who is correct? 64.236.121.129 (talk) 16:40, 28 November 2007 (UTC)
 * Well, the thing is, if someone sneezed in a building, the viruses do not go away immediately, correct? So, if someone walked through the sneezed area, there will be a higher concentration of viruses in that particular area, which means there can be viruses in the air, especially in an enclosed public building. Also, viruses can live on uncleaned surfaces for days, so if you touched the surface and rubbed your nose, some viruses might enter your nose. What I also meant was, there can be viruses inside you, although they are usually controlled so you don't get sick. Sorry if you misunderstood, and I'm not really an expert, so make sure you understand that when you're deciding the general answer to your question. Hope this helps. Thanks. ~ A H  1 (TCU) 18:45, 28 November 2007 (UTC)
 * Let's clear up a few things. Some viruses, like HIV need bodily fluids to survive and are destroyed on contact with air, while other viruses can live briefly outside of the body, like cold and flu viruses, some of which can survive up to about 48 hours depending on conditions.  Also, "patient zero" generally refers to the first/main person who caused the disease to spread within a population, which is not necessarily the person who spread it to you.  Finally, viruses cannot reproduce without a host.  What this means is that any viruses in the environment come from another host, though that host may not be a human.  This is not a contradiction, it's just neglecting to mention that the "viruses around us" come from other living things. --  Hi  Ev  03:39, 2 December 2007 (UTC)


 * I didn't read the whole thread but a few points to mention. It has been suggested although as far as I'm aware is completely unproven that people may have slightly weaker immune systems in cold weather and also that viruses may last longer in the environment which are some of the reasons why cold and flus are more common in winter. In any case, it's generally accepted that the closer contact between people etc in the winter season are the primary reasons. Bear in mind it AFAIK isn't just winter, cold and flus tend to be more common in the rainy season in tropical countries when it's colder (although to a far less degree) and people also spend more time in close quarters. Nil Einne 08:40, 1 December 2007 (UTC)

Reflection of voltage/current ???
Hi, I was reading web(including wikipedia) articles on what the characteristic impedance aka 75 ohms mean, and some related stuff about transmission. I've seen and how generic waves reflect a part of their energy (at the interface) when they enter a medium of different 'elasticity' than in which they were traveling. But I don't understand how electricity(or any wave for that matter) can reflect off an interface of different impedance. Can some one direct me to a wiki/web page which deals with this sort of reflection of current/voltage as i don't know how any technical terminology to search with. I haven't so far dealt with electric fields inside conductors and their role in conduction and I find it confusing to think about infinitely long conductors and effect of transmission being non-instantaneous. 59.93.3.188 (talk) —Preceding comment was added at 15:55, 26 November 2007 (UTC)
 * See impedance matching, standing wave, and standing wave ratio. These aren't much help, admittedly. Remember that it's the impedance of the load we care about, and that depends on frequency. If it matches, all the energy will be taken up. You can see the load sort of like the physical equivalent spring-and-mass system. If the load fails to use up the power, it has to go somewhere, so it reflects back and forms standing waves in the transmission line. A wave in a jumprope is an honest-to-goodness wave just like an electromagnetic one, at least as far as power transmission goes. This is a dumbed-down version, not because I think you're dumb, but because I have forgotten most of it. --Milkbreath (talk) 16:21, 26 November 2007 (UTC)
 * Howdy mean, Milky, they aren't much help? I find them quite enlightening. Do you have any suggestions on how they might be improved? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 01:42, 28 November 2007 (UTC)
 * I was hoping for a down-and-dirty walkthrough of power reflection, which was the original question. The impedance matching article blows right by that as if it's self-evident. Power is reflected?!!! What the hell does that mean, we ask ourselves, and we're left to imagine it. I used to be a First Phone, but even back when I had a clue, transmission lines and antennas seemed like magic to me. "Thou shalt build the antenna 2.7 cubits by 3.31 cubits by the square root of five cubits...." It's pure math, pure applied theory. So I can tell when I'm not being told something, but that's about it. --Milkbreath (talk) 03:00, 28 November 2007 (UTC)


 * Seen reflection coefficient yet? —Preceding unsigned comment added by TreeSmiler (talk • contribs) 03:03, 28 November 2007 (UTC)


 * Rather than thinking about electrical signals, you might want to think about electromagnetic energy of a shorter wavelength: light. When it is travelling in a material of one impedance (which optics folks tend to call refractive index) and it meets material of a different refractive index, some of the light is transmitted into the new material but the rest of the light (that wasn't transmitted) is reflected back. Electrical impedance works the same way; when the impedance changes, a reflection occurs. For radical changes of impedance (to an open circuit or a short circuit), the entire electrical wave is reflected back to the source. You might also enjoy our articles about time-domain reflectometry and the time-domain reflectometer.


 * Atlant (talk) 16:33, 26 November 2007 (UTC)

Possible to destroy a virus by smashing it?
If you knew a virus was on a stone, and you took a sledgehammer and you smashed the area it is in, is it possible to destroy it? 64.236.121.129 (talk) 15:58, 26 November 2007 (UTC)


 * Localized heating of the impact area might denature your virus, destroying it. But I think it would be a very chancy thing, with a good chance of aerosolizing virions as well, so if you thing there is, say, some Captain Trips on the rock, why not just walk away?


 * Atlant (talk) 16:28, 26 November 2007 (UTC)


 * Of course you should just walk away. But that's not what my question is. 64.236.121.129 (talk) 17:00, 26 November 2007 (UTC)


 * Viruses are very, very small. So small that when you are talking about mechanically smashing them, you have to think about how tight a seal it is going to be. Your hammer, no matter how smooth it might seem, has lots and lots of imperfections and the odds are that you're not going to smash it. Even very small bugs (e.g. fleas) are incredibly hard to smash for this reason (along with the fact that they have slippery shells that are meant to make it hard to smash them). Something as small as a virus, I would say that your odds of actually making contact with it are very minimal. --24.147.86.187 (talk) 16:57, 26 November 2007 (UTC)
 * I agree. Hmm. But if you had, say a nanomachine on the scale of a virus, and it went up to the virus and ripped it up, it would die then right? 64.236.121.129 (talk) 17:00, 26 November 2007 (UTC)


 * It's arguable whether the virus was "alive" before you smashed it. But yes, if it can move xenon atoms around to spell IBM, then something like an atomic force microscope or scanning tunneling microscope could probably "dismantle" a virion.


 * Atlant (talk) 17:25, 26 November 2007 (UTC)
 * Your problem will not just be one virus, but there could easily be 1000000 viruses on your stone. Even if you destroy 90% you still have 100000 infectious particles. Graeme Bartlett (talk) 20:09, 26 November 2007 (UTC)


 * The goal would be making a manmade virus that is attracted to a certain virus and then restructures that virus to clone the manmade anti-virus virus. So, every time the manmade virus meets a virus it is supposed to kill, it actually makes another one of itself to fight off the entire virus population.  I wonder if there'll be enough D&D fans on the team that invents this to give a name that references the charm spell used to make enemy monsters fight for you. --  k a i n a w &trade; 20:23, 26 November 2007 (UTC)


 * Sounds like a really big prion. (sorry, not a D&D fan.) Someguy1221 (talk) 20:50, 26 November 2007 (UTC)


 * Well, viruses can't reproduce by themselves - they need the facilities of a host cell in order to reproduce (think like the aliens in the movie "Alien"!) - that's why they are arguably not 'alive' at all. So if your manmade "virus" is truly a virus and not some other form of science-fiction nanotechnological assembler - then it can't really make copies of itself at will like that.  But even a nanotech assembler would need energy and raw materials in order to make a copy of itself.  That would likely be a time-consuming thing compared to the time a virus needs to reproduce (if it has a host).  So whilst it may one day be possible to build tiny robots that can shred viruses mechanically, I doubt they'd do it by duplicating themselves and then committing suicide in order to take down their opponent.  However, since we have no way to build such machines - nor any real certainty that they'll actually be possible at all - it's tough to speculate. SteveBaker (talk) 21:05, 26 November 2007 (UTC)


 * Smashing? Well, no, but then smashing isn't really good at destroying things anyway.  Smashing a piece of wood and you get lots of little pieces of wood.  Smash a rock and you get smaller rocks, etc.  But smashing does little to change the basic nature of the substance.  However if we are going to try sterilize with machine shop tools, I bet an arc welder would be pretty effective.  More ambigously, I wonder how well an angle grinder would do at killing virii?  If you grind down a surface, I'd lay good odds that most of the virii that were removed (at the least).  Dragons flight (talk) 21:25, 26 November 2007 (UTC)

Why do I get cold after I eat?
Sometimes it's said that people get drowsy after lunch (or any big meal), because 'the blood goes to the stomach to aid digestion'. I don't know if that makes sense or not. I do know that I seem to get cold after I eat, which corresponds with my recollection that it always seems colder outside when one goes back on the ski slope after lunch. So, the question is, does it make sense, physiologically, that the body sends extra blood to the stomach to aid digestion, and this takes blood away from the task of keeping me warm? Are there other physiological functions that would be impacted in the same way, after eating? I know of someone who claims that its harder to keep an erection after eating a big meal...would it be the same story? —Preceding unsigned comment added by 213.84.41.211 (talk) 16:30, 26 November 2007 (UTC)
 * The sensation of warmth and cold is most directly related to how cold your skin is. So if the body does indeed direct an overly large amount of blood to your digestive system to the detriment of blood flow to your skin, then your skin will certainly feel colder, though this says nothing about your internal body temperature. Someguy1221 (talk) 16:41, 26 November 2007 (UTC)
 * One factor in getting sleepy when you eat is serotonin, which comes from 5hydroxytryptophan which comes from tryptophan which as is widely known comes from food. But, everybody gets it wrong; tryptophan is an amino acid and comes from protein, but it's relatively rare with respect to the other amino acids so that the presence of a lot of protein to be digested causes a lot of competition and saturates the transport sites and it actually gets taken up less. In fact, more carbohydrates in the meal causes serotonin to go up, and drowsiness. So it's not the turkey on thanksgiving. Judith Wurtman at MIT did a bunch of work on this for the defense department, who were interested in questions like how to make sure the folks with their fingers on the triggers in the missile silos wouldn't fall asleep. she found some folks who were so sensitive they couldn't stay awake after the highcarb lunch, period. other folks had a self-medicating thing, i.e. got really antsy midafternoon if they couldn't get a carb break. here's a couple of general public type refs: http://www.fastcompany.com/magazine/06/diet.html http://www.healthsystem.virginia.edu/uvahealth/news_mindbody/0610mb.cfm Gzuckier (talk) 21:50, 26 November 2007 (UTC)

Metal case enclosure heat transfer coefficient
What would be a good way to calculate the capacity of a metal case to dissipate energy by natural convection.

I'm thinking of building a case 20 x 15 x 10 cm in aluminium and would like to know how much heat can be produced inside without overheating. The internal temperature would probably be 40-45 degrees and the maximum external temperature 35 degrees.

Most of the websites I've seen don't offer a simple way to calculate the convective heat transfer coefficient of the walls.

I'm guessing 50W might be the limit at 35 degrees outside and maybe 80W at 20 degrees. --Jcmaco (talk) 16:40, 26 November 2007 (UTC)


 * It would depend a lot on whether the internal and or external air is stirred by a fan or left to natural convection. For the convective situations, it would also depend on the orientation of the enclosure. Normally, to dissipate 50W, you'd want some method to directly couple the heat source to the aluminum enclosure. You can experiment with all of this rather easily by using resistors as the heat source and your favorite thermometer (thermocouples, thermistors, infrared thermometer, whatever) as the measuring device(s).


 * Completely off-the-cuff, managing to dissipate 50W and achieving a 10C temperature differential using only natural convection sounds optimistic to me; I'll bet you'll at least need cooling fins on the outside of the case.


 * Atlant (talk) 16:45, 26 November 2007 (UTC)


 * The heat transfer coefficient is not easily calculable from what you have, so you may have to run an experiment first using the relevant equations from that article. We can do an estimate, but to start we need two things: Newton's Law of Cooling $$T=T_e + (T_0 - T_e) e^{-k t}$$ with k predetermined for aluminum in air (try google or experiment, or just set = 0.5), and the Heat law $$Q=\sum m c\Delta T$$, with the specific heat c being widely available for both aluminum and air (both are about 1 J/g/K). Now we take the time derivative and get $$dQ/dt=P=\sum m c (-k(T_0-T_e)e^{-k t})$$ for our power dissipation, then set that equal to $$dQ/dt=h A (T_0-T_e)$$ and we get our heat transfer coefficient $$h= -(k/A)e^{-k t} \sum m c$$.
 * Now let's say we're adding power P0 to the system, from whatever's heating your case. Equilibrium then occurs where $$dT/dt=0$$, or $$P0 = dQ/dt = h A (T_0 - T_e)$$, which you can plug in values for at t=0. SamuelRiv (talk) 21:45, 26 November 2007 (UTC)

What metal is the worst conductor of heat?
^Topic 64.236.121.129 (talk) 17:04, 26 November 2007 (UTC)

There's a chart here: http://www.engineersedge.com/properties_of_metals.htm --JDitto (talk) 19:10, 26 November 2007 (UTC)


 * According to that chart, it's stainless steel - which suprises me a lot - but in any case, that's kinda cheating because there is a ton of (non-metallic) carbon in steel so it's really not a pure metal. In terms of pure metals, Lead wins the prize - which is about what I'd expect - lead is nowhere near as "cold to the touch" as most other metals (which is a good quick way to guess what the thermal conductivity of a material is).  That chart seems to cover only the more common engineering metals - whether you'd find that something weird like metallic liquid hydrogen or one of the transuranics had a lower coefficient is hard to guess. SteveBaker (talk) 20:54, 26 November 2007 (UTC)


 * Mercury has a lower thermal conductivity, though I don't know whether that would hold true when it was solid. In either state, I'd guess it's not practical for any application you'd be considering. jeﬀjon (talk) 21:41, 26 November 2007 (UTC)


 * According to this list of the thermal conductivities of all elements, neptunium is the worst conductor of heat amongst the metal elements, followed by plutonium and manganese. --Bowlhover (talk) 00:27, 27 November 2007 (UTC)

How does stainless steel compare to say... Concrete or stone? 64.236.121.129 (talk) 14:41, 27 November 2007 (UTC)


 * Concrete conducts heat MUCH less well than stainless steel. The coefficient of conductivity for steel is around 14 to 16, for concrete it's 0.8 to 1.3.  For comparison, metals like copper and silver that conduct heat very well have coefficients up around 400. But check our article List of thermal conductivities - it has an extensive list. SteveBaker (talk) 17:01, 27 November 2007 (UTC)

Quartz
Hello

My queastion is as follows. I found a geod near the town I live in, upon opening it the cyrstal inside was a light, medium brown. I looked through the entire area of this site on quartz cyrstal and did not see the same crystal. So i would like to know if there is a possability that someone could tell me what variety it is. Thank you. --63.245.189.4 (talk) 17:18, 26 November 2007 (UTC)

Your talking about a geode right? This site, has several brown crystal geodes, each one described as calcite crystals. Check out the 2nd picture in the calcite article to see if it's similar to yours. --JDitto (talk) 19:08, 26 November 2007 (UTC)
 * Quartz in geodes is often coated by iron oxide, making it look brown. Cheers Geologyguy (talk) 22:04, 26 November 2007 (UTC)
 * Smoky quartz is brown. DuncanHill (talk) 09:04, 27 November 2007 (UTC)

Spacetime Dipping
According to general relativity all masses make a dip in the sort of sheet of space time, making a potential well, and thats how masses have gravity. But if two massive particles, say a low energy electron and positron annihilate, what happens to the 'dips' in space time that they both have, seeing as the energy is carried away by two photons which do not have mass anywhere equivalent to the electron positron pair. ΦΙΛ Κ 20:23, 26 November 2007 (UTC)
 * I'd suspect the mass would be converted into energy. No mass, no gravity well. --Kjoonlee 20:41, 26 November 2007 (UTC)


 * Actually, the photons will have mass exactly equivalent to the electron/positron pair (if we're talking about relativistic mass, that is). Someguy1221 (talk) 20:48, 26 November 2007 (UTC)
 * Ok, almost exactly. Maybe some gets radiated as EM waves, maybe a tiny bit as gravity waves.  Someguy1221 (talk) 20:49, 26 November 2007 (UTC)


 * But if there is some loss, does this require some instantaneous movement of space time to account for this, to just sort of instantly pop into a different shape to coincide with the annihilation ΦΙΛ Κ  21:13, 26 November 2007 (UTC)


 * Not at all. At the the "moment" right after annihilation has two photons with the same mass and approximate position as the two particles that preceded them.  As far as spacetime curvature is concerned, nothing has really changed.  When I referred to loss, these would be gradual losses as the two particles approach, not at the moment they annihilate. Someguy1221 (talk) 21:18, 26 November 2007 (UTC)


 * Mass-energy is conserved, and mass-energy is the source of spacetime curvature in GR, so the shape of spacetime immediately before the interaction is the same as its shape immediately after. —Keenan Pepper 21:46, 26 November 2007 (UTC)


 * Heh, I should have known better. :) --Kjoonlee 22:47, 26 November 2007 (UTC)

Calcium carbonate from breathing into a solution
I recently performed a scientific experiment. We were, in class, given a filtered solution of what I believe to be some kind of "chalk water". This was put in a glass, and once one breathed into it through a straw, calcium carbonate would form and settle at the bottom (with time). My question is then, what was the solution I added CO2 to? And I assume that, in order to balance the equation, H2O must be added (so it is CO2 + ? = CaHO3 + H20)?

This is not a homework question, I've simply forgotten what the equation went like =) Also, my teacher balanced it the wrong way, saying in fact that calcium carbonate is CaHO2. Thank you for your help! 81.93.102.185 (talk) 22:30, 26 November 2007 (UTC)


 * Your equation can't be right - you have a carbon atom on the left side - but no carbon on the right. Oh - I see.  You said that Calcium Carbonate was formed...that's CaCO3.  Anyway, the answer is in our Calcium Carbonate article Ca(OH)2 + CO2 → CaCO3 + H2O - so the missing ingredient is Calcium hydroxide.  Woohoo! Steve gets to answer a chemistry question!  With a more than 1% chance of being correct! SteveBaker (talk) 22:54, 26 November 2007 (UTC)


 * (after edit conflict) The unbalanced equation would then be CO2+Ca(OH)2
 * --> CaCO3 (note that calcium carbonate is CaCO3, not CaHO2). Since water is neither created nor used up during the reaction, I don't think it is not part of the equation; it simply helps the reaction.  --Bowlhover (talk) 23:03, 26 November 2007 (UTC)


 * Sorry, water is created during the chemical reaction. The balanced equation would then be Ca(OH)2 + CO2 --> CaCO3 + H2O.  --Bowlhover (talk) 23:17, 27 November 2007 (UTC)
 * Otherwise it would act similar to spectator ions. 81.158.37.78 (talk) 23:14, 29 November 2007 (UTC)

What is the biological basis for appreciation of music?
That is, what is it in our genes that makes us react to a pattern of arbitrary sounds? —Preceding unsigned comment added by Xhin (talk • contribs) 22:50, 26 November 2007 (UTC)
 * Honestly, I'd be surprised if anyone had anything other than speculation and a few unconnected tidbits of information on this topic at this point in time. The brain and genetic expression are probably the two biggest mysteries left in explaining how organisms work.  Toss in the rather subjective appreciation of auditory beauty and you're asking for something that is at the far boundaries of human knowledge.  Good luck on your quest for an answer. --  Hi  Ev  23:08, 26 November 2007 (UTC)


 * I agree that we don't know for sure - but one thing that's interesting is the mathematical basis of many musical systems. The fact that we like music where there are simple mathematical relationships between the frequencies and durations of the notes cannot be a mere coincidence.  I suspect this has something to do with it - but precisely what is uncertain. SteveBaker (talk) 23:16, 26 November 2007 (UTC)


 * Unless the mathematical aspect of music is simply Emergent. -=- Xhin -=- (talk) 23:27, 26 November 2007 (UTC)


 * Try music theory. The mathematics of musical perception are a subject of continuing research, but it is fairly well understood how thirds, fifths, octaves and inversions make up the geometry of music. Physically, our cochlea does something similar to taking a Fourier transform of the sound waveform, giving us a range of frequencies that harmonize according to mathematical rules. Thus chords sound like the fundamental, etc. Chord progressions are not well understood, but there is some very promising research by Dmitri Tymoczko on their geometry based on 2, 3, and 4 dimensional topological mappings of the chord symmetries. See . SamuelRiv (talk) 23:52, 26 November 2007 (UTC)


 * I worked on a research project a few years ago: "Can a computer tell the difference between pleasing and non-pleasing music?" Yes - it can. This was based on the realization that many "zipfian" distributions exist in "pleasing" music. Since the same balances exist in pleasing poetry, paintings, and throughout nature, it is possible that our brains pick up the natural balance and "appreciates" it. If you are interested in the research, it is here. -- k a i n a w &trade; 23:54, 26 November 2007 (UTC)


 * The only problem with that is the subjectivity of music appreciation -- for example, I've heard songs which somehow got record labels, but sound like cacophany to my ears. Anyway, you guys are helping -- slowly. Keep it up! -=- Xhin -=- (talk) 00:16, 27 November 2007 (UTC)


 * It probably poses more questions than it answers, but Oliver Sacks' book, Musicophilia: Tales of Music and the Brain offers a fascinating insight into the neural coding for music and its appreciation. Here is a podcast of Sacks talking about it (he addresses the question of subjectivity too). Rockpock  e  t  00:22, 27 November 2007 (UTC)


 * I've read reviews of that book, and I plan to be delightfully surprised to find it in my Christmas stocking. Another very good one is Music, the Brain and Ecstasy by Robert Jourdain.  Re cacophony, I was going to make the point that it's fascinating how a computer can distinguish between pleasing and non-pleasing music but many humans seem incapable of so doing (and here I'm thinking of things from post-Schoenbergian squarks to heavy metal) - but then, it's all subjective, and what I enjoy would be rubbish to someone else, I guess. --  JackofOz (talk) 00:33, 27 November 2007 (UTC)


 * Appreciation of a particular sequence of pitches? Doubtful. But given that an appreciation of music something found in countless cultures throughout time and location (and I do believe Brown included music in his list of Human Universals). It seems likely that there is a biological basis for this universal appreciation.--droptone (talk) 02:21, 27 November 2007 (UTC)

How do you derive the properties of chemistry (ie, flowing liquids) from physics?
Unloaded question, but much help appreciated ! -=- Xhin -=- (talk) 22:51, 26 November 2007 (UTC)


 * You solve the quantum mechanical equations for material...Computational Chemistry may help.Shniken1 (talk) 23:24, 26 November 2007 (UTC)


 * By far the greatest success in understanding physical chemistry has been statistical mechanics for molecular structure combined with quantum mechanics for atomic structure and electrodynamics for interaction. Flowing liquids, for example, are described quite well by Bernoulli's principle, which can be derived statistically. The ideal gas law is very simply derived from first principles in stat mech as well. For a good, thorough book on the subject, see Thermal Physics by Kittel and Kroemer. SamuelRiv (talk) 23:56, 26 November 2007 (UTC)

Failing audio cables
I have a lot of trouble with audio cables 'breaking'. I use various types of these a lot for connecting musical instruments, amps, speakers, mics, computers etc such as mic leads, jack leads, RCA leads anbd various combinations. For example the 3.5mm stereo jack to double mono RCA lead I use to connect my laptop to my main PC's speakers (as the laptop's speakers are vey poor) has just started playing up, I only so much have to breathe on it and one side of the stereo signal cuts out, when I wiggle it near the jack plug, the dodgy side cuts in and out although the other side is OK (I have been testing it by shifting the balance to the affected channel only).

I know the easy answer is simply to buy a new cable which in this case is fairly cheap but when £10 mic leads fail it is no joke and it seems a waste to keep buying new leads. I just wondering what actually causes these leads to fail? I presume they are made of copper wire which somehow breaks but why is it such a problem with audio/video leads? I have never had this problem with mains leads or any other type of lead, ie USB, parallel, firewire etc and as the latter types are digital rather than analogue, I would have thought broken wires would cause more problems than with analogue leads. I don't exactly pull on the leads, I coil them up when not in use but not tightly so I can't think that I am doing anything beyond what they are designed for.

Secondly, is it possible to repair them? Obviously, this depends on what the actual problem is! GaryReggae (talk) 22:53, 26 November 2007 (UTC)


 * Mine always fail from other bending so I suspect it is something to do with this. Perhaps a little more slack would reduce wear, or perhaps higher-quality cable would be more sturdily built. I was told to loop them together up/down against each other to stop wear. When it's occurred to me it has always been near the headphone socket/headphone so I guess it must be strain/stress and bending that is causing it. Not sure if it is repairable, I would expect for the cost it wouldn't be worthwhile. ny156uk (talk) 23:09, 26 November 2007 (UTC)


 * Generally, it's just because the wire is bending a lot. If you take a piece of wire like a paperclip and bend it back and forth over and over, eventually, it'll break.  Copper is pretty flexible - but eventually, it goes.  Probably the wire at your laptop end broke because it's being moved more often (or plugged and unplugged more often) than the ends at the speakers or whatever.  You can mend those wires reasonably easily - there are two approaches.  Firstly, if you can tell where it's broken (usually within an inch or two of the connector) then cut the wire an inch or so beyond the break - get a wire stripper (or a pair of scissors if desperate) and now you need to re-attach the connector.  There are three approaches:
 * Cut the wire on the other side of the break, strip those wires - then twist the ends together and wrap them up with a few inches of electrical tape so they don't short out. This isn't 100% the best thing - and if the break is too close to the connector, you can't do it this way - but it's very easy and gets you going with no tools more sophisticated than scissors and electrical tape!
 * Carefully remove the plastic shroud on the connector and thread it onto the cut/stripped side of the wire. De-solder the short bits of wire from the connector, solder on the new ends and replace the shroud.  Of course this assumes you have a soldering iron (and possibly a desoldering gun) along with the necessary skills to do it.  I suspect you don't or you wouldn't be asking...but hey - we all had to learn sometime!
 * Go to your local Radio Shack (or whatever national equivelent you have) - locate the rows of little, beautifully labelled drawers - find a connector that looks like the one you cut off BUT WHICH HAS SCREW CONNECTIONS instead of solder joints. Now you can wrap the stripped ends of wire around the screws and tighten them up.  This is easy and has one HUGE advantage over the other two ways.  When the wire breaks AGAIN (as I'm sure it will), you can just trim off a bit more wire and fix it again with no more tools than a screwdriver and a wire stripper (or scissors if you are careful!).
 * Good luck! SteveBaker (talk) 23:13, 26 November 2007 (UTC)


 * Thanks Steve, I will try fixing it later, the break seems to be right by the jack connector and it's a moulded plastic one so I think I'll just go to Maplin's and buy a new plug with screw fittings if they have them as I'm not very good at soldering. As you say, the next time it breaks, probably in the same place near the connector, it will be easy to fix! GaryReggae (talk) 09:07, 27 November 2007 (UTC)


 * Actually, if it does break often, some kinds of connector come with strain relief widgets. These take the form of a long plastic or rubber sleeve that covers the wire out to a distance of a couple of inches out from the connector.  Others are like a stiff spring that you thread over the wire+connector.  They take some of the load off the wire and prevent it from bending unnecessarily.  If you are buying a new connector - you might look to see if any of them have superior strain relief. SteveBaker (talk) 16:51, 27 November 2007 (UTC)